The need for manufacturing pipes or tubes coated with thin films on their outer and/or inner walls, or for coating wires, can arise in many situations. Deposition of simple materials can be performed using currently available thin film deposition methods. However, for complex multicomponent materials (i.e., ternary or quaternary compounds, etc.) these techniques are generally unsuitable due, for example, to differential evaporation or sputtering rates. Also, traditional deposition techniques which can be utilized are cumbersome to use in practice due to the need to provide electric or water leads to the target region which would be located within the pipe to be coated. Chemical vapor deposition techniques, which could, in principle, be simple to use for some materials, have the disadvantage of requiring much higher temperatures than the pulsed laser deposition (PLD) technique employed in accordance with this invention.
PLD has proven to be a powerful thin film growth technique, particularly for multicomponent materials, such as complex oxides. However, PLD is commonly used to deposit materials onto flat, and usually small, substrates. In contrast, the method and apparatus presented here allows the use of PLD to deposit thin films on inner or outer cylindrical surfaces, such as pipe or tubing walls or on wires. Materials for which there is an interest in coating wires or external walls of pipes are high-critical-temperature (high-Tc) superconductors, such as Yttrium-Barium-Copper-Oxide (xe2x80x9cYBCOxe2x80x9d) and other ceramic cuprates. PLD has been used to produce quality high-Tc ceramic films such as YBCO-coated metallic (Nixe2x80x94Cr alloy) tapes. This technique is useful because it allows the tape surface to be prepared by deposition of a xe2x80x9cbufferxe2x80x9d layer by PLD before the actual tape is deposited.
Despite the advances made in producing such tapes, wires would probably be preferred over tapes because the systems in which these materials can be used, e.g., electromagnets, motors, generators, power transmission lines, and transformers, can be more easily built using wires, or bundled wires (stranded cables). For transformers in particular there can be a very large market in the near future, as most power line transformers in the United States are approaching the end of their useful lives. Power generation utilities are apparently very interested in superconducting transformers, even if they must be immersed in liquid nitrogen.
First generation high-Tc superconductors presently being used are powder-in-tube devices based on Bi2Sr2CaCu2Ox (BSCCO) material. While such devices do not lend itself to very many applications, kilometer-length tube pieces are currently produced commercially. However, BSCCO loses its superconductivity at modest magnetic fields. YBCO is a much better superconducting material, but cannot be used for powder-in-tube fabrication. Sintered, fully reacted YBCO pieces cannot be easily produced in very large or complex shapes, and, more importantly, are not flexible. Thin film-coated flexible pieces appear to be the best option for device application of YBCO in a large variety of situations.
Another area of interest is the application of diamond-like carbon (DLC) coatings to surfaces. DLC coatings can be useful for tribological applications, such as for enhancement of wear-resistance. Besides DLC, there are many other hard materials, such as carbides and nitrides, for which the PLD process is suitable. The methods presented in this disclosure could be readily applied to coat surfaces with cylindrical geometry, such as drill bits, shafts, motor pistons and cylinders.
A further use which is contemplated based on the methods presented in accordance with this invention is the coating of wires with materials exhibiting colossal magneto-resistance CM R, particularly the perovskite manganese oxide La1xe2x88x92x CaxMn03 (similar to the copper oxides exhibiting superconductivity, but with manganese instead of copper). These materials, which are complex oxides, can be best applied via PLD. As these CMR materials were only recently discovered, technologies based on it are not yet fully developed, but there is much interest in relation to device applications based on ferromagnetics.
The present invention relates to an apparatus that allows the use of Pulsed Laser Deposition (PLD) to deposit thin films on inner cylindrical surfaces, such as inner pipe or tubing walls. In addition, the present invention relates to new methods for applying thin film coatings on outer surfaces of cylindrical objects. Specifically, the disclosed apparatus and methods rely on the PLD technique for the actual coating. These PLD techniques are particularly pertinent for coatings consisting of multicomponent inorganic materials, such as superconducting ceramics, or for materials which benefit from non-equilibrium growth conditions, such as diamond-like carbon (DLC).
In accordance with the present invention, when the materials to be deposited are on the inner walls of a pipe, a high power pulsed laser beam is caused to converge towards a target surface which is subsequently ablated by the laser beam. The target is located within the pipe to be internally coated, and at an inclination with respect to the system""s axis, being defined as the symmetry axis of the pipe. As the material ablated from the target is deposited on the pipe wall, relative angular and longitudinal motion between the pipe and the target is produced, so that the wall is sequentially coated.
When materials are to be deposited on the outer walls of a wire or pipe, or the inner walls of a pipe in a symmetric fashion, the laser beam is shaped by suitable optics into a conic beam incident onto a conic target surface which is subsequently ablated by the laser. The cylindrical geometry is such that a cylindrical work piece, e.g., a rod, pipe, or wire, can be coated uniformly along its inner surface by the plume emitted by the target, while the work piece is translated along the axial direction.
The present invention is directed to a pulsed laser deposition method for uniformly depositing at least one material on an outer wall of a pipe. The method comprises passing a pulsed laser beam through at least one lens such that the laser beam is caused to converge towards a target surface. Once incident on the target surface, the beam will ablate the target surface. The target surface is preferably located within a pipe that is to be internally coated, and is at an inclination with respect to the symmetry axis of the pipe. In addition, a relative angular and longitudinal motion can be produced between the pipe and the target so that the wall can be sequentially coated. This method can occur either in a vacuum or in a low-pressure atmosphere, optionally other than air. Depending on the material to be coated, the inner wall to be coated can also be heated above room temperature.
The present invention is also directed to a pulsed laser deposition method for uniformly coating at least one material on an inner wall of a pipe or rod in a symmetric configuration. This method can be adapted for coating both outer walls of a pipe or rod, or flexible wires. The method comprises passing an axially symmetric, pulsed laser beam through appropriate optics that shape the beam into a cone or truncated cone. The optics used to form such a shape comprise at least one negative conical lens and at least one spherical converging lens. The symmetric configuration of the deposited material is a result of the collinear configuration between symmetry axes of a target surface and the lenses. To ablate the target material, the laser beam is subsequently converged towards the target surface. The cone or truncated cone shaped beam incident on the target material produces a plume of evaporate material also having a conical shape. By placing the rod, pipe or wire to be coated with its longitudinal axis coincident with the symmetry axes, the rate of evaporate material incident on the wall is substantially the same for every direction in the plume.
Depending on the material to be coated, the walls to be coated can again be heated above room temperature. In addition, when flexible wires are to be coated, the above method can be modified to allow for the continuous supply of wires from a reel by at least one pulley or channel, which guide the wire through the symmetry axes.
In addition, the present invention is directed to an apparatus for depositing at least one material on an inner wall of a pipe or rod, or on a wire. Such an apparatus comprises a laser capable of producing a pulsed laser beam, a target material a optionally positioned at an angle inclined to the symmetry axis of the pipe, rod or wire to be coated, and at least one lens which concentrates the beam onto the surface of the target material. The apparatus further comprises a chamber having at least one feed-through port and at least one window, wherein the chamber is capable of holding a vacuum, and optionally contains a heater assembly.
When deposition of a material in a symmetric configuration is desired, the lens assembly can be modified to include at least one negative conical lens and at least one spherical converging lens wherein said lenses shape the resulting beam into a cone or a truncated cone shape.
When flexible wires are to be coated, the above apparatus can be modified with a system that continuously guides the wires. For example, the continuous supply of wires from a reel can be accomplished by at least one pulley or channel, which guide the wire through the symmetry axes.